Augmentation of thyroid-stimulating antibody-stimulated cyclic adenosine monophosphate response by polyethylene glycol, polyvinyl alcohol, and dextran; highly sensitive porcine thyroid cell thyroid-stimulating antibody assay

SENSITIVE THYROID-STIMULATING ANTIBODY ASSAY WITH HIGH CONCENTRATIONS OF POLYETHYLENE GLYCOL FOR THE DIAGNOSIS OF GRAVES' DISEASE

The aim of the present study was to determine the usefulness of a newly developed thyroid-stimulating antibody (TSAb) assay. We developed a highly sensitive TSAb (sTSAb) assay with 22.5% polyethylene glycol-precipitated crude IgG. The thyroid-stimulating hormone (TSH) receptor antibody (TRAb) causes Graves' disease and TRAb has been measured as TSH-binding inhibitor immunoglobulin (TBII) and thyroid-stimulating antibody (TSAb). The TSAb stimulates the thyroid glands and causes hyperthyroidism. In addition to investigating the usefulness of the newly developed sTSAb assay, we also investigated the frequencies of positive TRAb in thyrotoxic patients with subacute thyroiditis, painless thyroiditis or a solitary toxic nodule. We studied 700 untreated Graves' patients with hyperthyroidism and 923 normal controls. We also studied thyrotoxic patients with subacute thyroiditis, painless thyroiditis or a solitary toxic nodule. Conventional TSAb (cTSAb) and sTSAb were measured as TSAb, whereas porcine TBII (pTBII) and human recombinant TBII (hTBII) were measured as TBII. Levels of cTSAb and sTSAb were determined in 923 normal controls and 629 untreated Graves' patients and cTSAb and sTSAb were found to be normally distributed in normal controls, but not in untreated Graves' patients. Receiver operating characteristic (ROC) curve analysis demonstrated that cTSAb and sTSAb had high sensitivity and specificity for Graves' disease. Of the patients investigated, 96.5% of untreated Graves' patients were positive for sTSAb and/or pTBII. Some untreated Graves' patients who were negative for cTSAb were positive for sTSAb. Paired determinations of cTSAb and sTSAb were performed in 146 untreated Graves' patients. A positive correlation was found between cTSAb and sTSAb. Titres of sTSAb were higher than those of cTSAb and sTSAb had high sensitivity. Of the 35 untreated Graves' hyperthyroid patients who were negative for cTSAb, 18 (51%) were positive for sTSAb. Of the 36 untreated Graves' patients who were negative for hTBII, nine (25%) were positive for sTSAb. Some untreated Graves' patients who were negative for cTSAb were positive for sTSAb and some who were negative for hTBII and pTBII were positive for sTSAb. 5. Some thyrotoxic patients with subacute thyroiditis or painless thyroiditis were positive for TRAb. However, the frequency of TRAb-positive patients was low in this group. None of the patients with a solitary toxic nodule was positive for TRAb. In conclusion, sTSAb had higher sensitivity than cTSAb. Graves' patients who were cTSAb negative and hTBII negative could be sTSAb positive. The sTSAb indicates TSAb activity, but pTBII and hTBII do not necessarily do so. We recommended that the sTSAb is used in Graves' patients.

Detection of low titre TBII in patients with Graves' disease using recombinant human TSH receptor

OBJECTIVES

We evaluated thyrotropin-binding inhibitor immunoglobulin (TBII) in sera from patients with Graves' disease (GD) by using the new human recombinant TSH receptor (TSH-R) assay to determine if it is useful for the diagnosis and follow-up of GD.

PATIENTS

Serum samples from 25 patients with untreated GD, 24 with relapsing GD, 15 with GD in remission and 197 treated GD patients were examined. TBII was also measured in sera from healthy individuals (n = 69).

DESIGN AND MEASUREMENTS

TBII was retrospectively measured by using the conventional porcine TBII assay (pTBII) and the human recombinant TBII assay (hTBII). Specificity was adjusted at 97.5% for both assays by receiver-operating characteristic (ROC) plot analysis, resulting in cut-offs at 10.5% inhibition (hTBII) and 9.9% (pTBII). Sensitivity was 87% for hTBII compared to 52% for pTBII (P < 0.0001).

RESULTS

Even in pTBII-positive patients, hTBII values (57.6 +/- 26.1%) were significantly (P < 0.0001) higher than pTBII values (34.2 +/- 27.6%). When 139 pTBII-negative serum samples from patients with treated GD were examined, 97 samples (69.8%) were positive for hTBII. hTBII values (23.9 +/- 17.0%) were significantly (P < 0.0001) higher than pTBII values (4.1 +/- 3.3%). hTBII was positive in 13 of 13 patients who were taking antithyroid drugs but had normal serum TSH levels. When 19 serum samples from pTBII-negative untreated patients with GD were examined, 15 out of 19 (79%) were positive for hTBII. We also examined 24 patients with relapsing GD. hTBII was positive in 16 (64%) patients, whereas seven (16%) were positive for pTBII (P < 0.01). Positivity of hTBII in these untreated or relapsing GD patients was significantly higher than that of thyroid stimulating antibodies. We then examined TBII levels in 15 patients with GD in remission who had normal serum TSH values. hTBII was positive in seven patients at the time of blood withdrawal, and GD subsequently relapsed in three hTBII-positive patients in 6 months.

CONCLUSIONS

Low TBII titres can now be followed more accurately during the course of treatment, which will also allow better longitudinal studies on the importance of TBII for the diagnosis as well as the prognosis of GD with respect to remission or relapse.

Antithyrotropin receptor antibody: an update

Numerous studies have reported the characteristics and significance concerning antithyrotropin receptor antibodies (TSHR-Abs), which cause Graves' disease and in some cases primary hypothyroidism. However, many unsolved questions concerning those antibodies remain. Here, recent developments in the study of TSHR-Abs are reviewed based on three aspects: mechanisms of TSHR-Ab production, antibody binding epitopes, and clinical TSHR-Ab assays. Mechanisms of TSHR-Ab production are discussed from five points of view: aberrant expression of the major histocompatibility complex, dysregulation of T cells, molecular mimicry, bystander effect, and expansion of autoreactive B cells. Regarding epitopes, unique TSHR-Abs have been reported that may explain the complicated pathophysiology of patients with TSHR-Ab diseases. Finally, recent efforts to improve TSHR-Ab measurements are introduced. Such efforts will contribute to clinical examinations and treatments for thyroid diseases as well as experimental methods of thyroidology.